I've noticed how almost all students have a tendency to interrupt their greatest successes: in the midst of a vocal exercise, they'll suddenly pull the plug on their singing, just as something new and wonderful was beginning to happen. (Much to the consternation of the teacher!)
Why do we all do this? (Yes, I do it too in my lessons.)
It seems that we humans are programmed with a great aversion to being wrong. Unfortunately, we are not always right about what is wrong. (And we're often wrong about what is right.)
Our brains get used to whatever experiences we habitually give them; these experiences will tend to be interpreted as right, correct, desirable—even when they are less than optimal.
Conversely, a new experience, even when it is superior to your habitual one, gets interpreted by your brain as wrong. It's as if a warning signal goes off—CAUTION, approaching unknown territory! I suppose that long ago in our evolutionary history, when we presumably had not yet amassed the collection of detrimental habits we modern people typically carry around, most usual experiences were to be welcomed, and unusual, potentially dangerous ones were best avoided at all costs.
Let me reassure you that in a voice lesson, you are highly unlikely to encounter a dangerous situation. You just might, however, if we set things up correctly in an exercise, encounter a brand new register coordination. And if that happens, you might have to remind your brain that, even though this new coordination feels foreign and WRONG, WRONG, WRONG, it might just be a step in the right vocal direction.
In other words, keep on singing, even if it feels like a horrible mistake to you. (I will let you know if ever you are so far off-course that you need to cut an exercise short.) This uncomfortable new experience might indeed be a blooper, in which case we'll change our approach and take another stab at it. But, if we are lucky, it might prove to be a serendipitous advance in your technique that we will want to nurture and solidify. (It's my responsibility as the teacher to set up exercises so that, as you progress in your lessons, you experience more advances and fewer bloopers.)
In closing, let's ponder the words of the wise if slightly sardonic F.M. Alexander: Everyone wants to be right but no one stops to consider if their idea of right is right.